PS: I often think about switching to single installation of wp, your combination of plugins would be the only one working, as described by the author of the stuff in my links. So I don’t have to think about switching again.

Have you tested the solution I’ve mentioned? Just for your interest: I set up a naked wp 3.1. (single) with buddypress 1.2.8, BuddyPress xProfiles ACL, Capability Manager and WP Roles at Registration – works like a charm and requires no coding by hand.